This invention relates to new pyrimidine compounds which are useful as antiozonants for rubber, processes for their manufacture, and to their use in inhibiting the deteriorating effect of ozone on unsaturated polymers.
The novel compounds of the invention may also be useful as stabilizers in lubricating oils and greases and natural or synthetic fats and oils. Thermoplastic polymers may also be stabilized against thermal and oxidative degradation and viscosity breakdown during processing.
It is well known that ozone causes surface cracking of conventional highly unsaturated rubber vulcanizates when the rubber is placed under strain in an ozone environment. The most severe deterioration occurs when a small number of cracks are formed which grow rapidly into deep, disruptive fissures. These ozone cracks seriously shorten the serviceable life of the article.
The rubber articles which may achieve lower service lives through the use of the novel compounds of the invention include hoses, belts, airsprings, sheeting, seals, gaskets, mounts, bridge pads and other mechanical goods.
Chemical antiozonants have been developed which retard the formation of the ozone cracks occurring under static and dynamic conditions. Examples of antiozonants in common use include the substituted paraphenylenediamine class of compounds.
The use of the well known paraphenylenediamine materials has improved ozone protection under both static and dynamic conditions, however, even the best of the class just described have a very strong tendency to both stain and discolor. The term "stain" or "staining" is herein used to describe the characteristic of a material to diffuse through a polymeric substrate and discolor the adjacent surface. This diffusion staining is highly objectionable in most light colored rubber articles. In tires, which is the largest application in which the ozone protection is required, the tendency to diffusion staining of the aforementioned paraphenylenediamine materials is objectionable particularly in white sidewall type tires. Even in non-white sidewall type tires, the tendency of the materials to diffuse to the surface of the tire sidewall can be objectionable in that a brown, dull surface is created on the tire sidewall. This is aesthetically objectionable in that it detracts from the general jet black, smooth appearance of a new tire. It is obvious that in a white sidewall tire, the migration of the brown discoloring material to the surface of the white sidewall is highly objectionable and generally difficult to remove during cleaning of the tire surface.
An object of this invention is to provide an antiozonant material which is highly effective in protecting a highly unsaturated polymer substrate from ozone attack. A further object is to provide ozone protection in a static condition at very low levels and to protect the rubber article during extended aging conditions against ozone attack. Yet another object is to produce a compound which does slowly diffuse and does not produce an objectionable brown bloom.
The novel arylenediamine substituted pyrimidine compounds of the invention have provided exceptional long term ozone protection under static conditions. An advantage of the substituted pyrimidine compounds is that it produces a substantially non-staining antiozonant of high molecular weight. A further advantage is that it slowly blooms to the surface of the rubber article. A further advantage is that the pyrimidine compounds of the invention provide outstanding dynamic protection without the use of waxes preferably by blending said pyrimidine compounds with other known antiozonants and antioxidants.